This invention relates to products including gypsum as a major constituent and more particularly to a method of producing these products so that they are resistant to damage by water.
Normally gypsum products, for example boards for walls and the like, are manufactured in the following way: gypsum in the hemi-hydrate form is admixed with a predetermined quantity of water (known as the "water demand") to form a slurry of required consistency. To produce a board the slurry is fed between paper liners and formed into the correct shape in a mould. The setting process which is exothermic in nature then takes place and results in the hard gypsum product.
Attempts to waterproof the products have included the addition of bitumen/wax emulsion to the slurry. This has not proved very satisfactory, probably because the emulsifying agents effect the setting time of the gypsum slurry and the conversion of the gypsum hemi-hydrate to the di-hydrate.
An object of this invention is to provide an improved waterproofing method for gypsum products.